High octane unleaded aviation gasoline

ABSTRACT

An unleaded aviation fuel composition meets the requirements of the ASTM D910 specification. Furthermore, the unleaded aviation fuel compositions of the present invention exhibit reduced bladder delamination, improved materials compatibility such as reduced elastomer swelling and reduced paint staining, and improved engine endurance.

FIELD OF THE INVENTION

The present invention relates to high octane unleaded aviation gasoline fuel, more particularly to a high octane unleaded aviation gasoline having improved materials compatibility, reduced bladder delamination and improved engine endurance.

BACKGROUND OF THE INVENTION

Avgas (aviation gasoline), is an aviation fuel used in spark-ignited internal-combustion engines to propel aircraft. Avgas is distinguished from mogas (motor gasoline), which is the everyday gasoline used in cars and some non-commercial light aircraft. Unlike mogas, which has been formulated since the 1970s to allow the use of 3-way catalytic converters for pollution reduction, avgas contains tetraethyl lead (TEL), a non-biodegradable toxic substance used to prevent engine knocking (detonation).

Aviation gasoline fuels currently contain the additive tetraethyl lead (TEL), in amounts up to 0.53 mL/L or 0.56 g/L which is the limit allowed by the most widely used aviation gasoline specification 100 Low Lead (100LL). The lead is required to meet the high octane demands of aviation piston engines: the 100LL specification ASTM D910 demands a minimum motor octane number (MON) of 99.6, in contrast to the EN 228 specification for European motor gasoline which stipulates a minimum MON of 85 or United States motor gasoline which require unleaded fuel minimum octane rating (R+M)/2 of 87.

Aviation fuel is a product which has been developed with care and subjected to strict regulations for aeronautical application. Thus aviation fuels must satisfy precise physico-chemical characteristics, defined by international specifications such as ASTM D910 specified by Federal Aviation Administration (FAA). Automotive gasoline is not a fully viable replacement for avgas in many aircraft, because many high-performance and/or turbocharged airplane engines require 100 octane fuel (MON of 99.6) and modifications are necessary in order to use lower-octane fuel. Automotive gasoline can vaporize in fuel lines causing a vapor lock (a bubble in the line) or fuel pump cavitation, starving the engine of fuel. Vapor lock typically occurs in fuel systems where a mechanically-driven fuel pump mounted on the engine draws fuel from a tank mounted lower than the pump. The reduced pressure in the line can cause the more volatile components in automotive gasoline to flash into vapor, forming bubbles in the fuel line and interrupting fuel flow.

The ASTM D910 specification does not include all gasoline satisfactory for reciprocating aviation engines, but rather, defines the following specific types of aviation gasoline for civil use: Grade 80; Grade 91; Grade 100; and Grade 100LL. Grade 100 and Grade 100LL are considered High Octane Aviation Gasoline to meet the requirement of modern demanding aviation engines. In addition to MON, the D910 specification for Avgas has the following requirements: density; distillation (initial and final boiling points, fuel evaporated, evaporated temperatures T10, T40, T90, T10+T50); recovery, residue, and loss volume; vapor pressure; freezing point; sulfur content; net heat of combustion; copper strip corrosion; oxidation stability (potential gum and lead precipitate); volume change during water reaction; electrical conductivity; and other properties. Avgas fuel is typically tested for its properties using ASTM tests:

-   -   Motor Octane Number: ASTM D2700     -   Aviation Lean Rating: ASTM D2700     -   Performance Number (Super-Charge): ASTM D909     -   Tetraethyl Lead Content: ASTM D5059 or ASTM D3341     -   Color: ASTM D2392     -   Density: ASTM D4052 or ASTM D1298     -   Distillation: ASTM D86     -   Vapor Pressure: ASTM D5191 or ASTM D323 or ASTM D5190     -   Freezing Point: ASTM D2386     -   Sulfur: ASTM D2622 or ASTM D1266     -   Net Heat of Combustion (NHC): ASTM D3338 or ASTM D4529 or ASTM         D4809     -   Copper Corrosion: ASTM D130     -   Oxidation Stability—Potential Gum: ASTM D873     -   Oxidation Stability—Lead Precipitate: ASTM D873     -   Water Reaction—Volume change: ASTM D1094     -   Electrical Conductivity: ASTM D2624

Aviation fuels must have a low vapor pressure in order to avoid problems of vaporization (vapor lock) at low pressures encountered at altitude and for obvious safety reasons. But the vapor pressure must be high enough to ensure that the engine starts easily. The Reid Vapor pressure (RVP) should be in the range of 38 kPa to 49 kPA. The final distillation point must be fairly low in order to limit the formations of deposits and their harmful consequences (power losses, impaired cooling). These fuels must also possess a sufficient Net Heat of Combustion (NHC) to ensure adequate range of the aircraft. Moreover, as aviation fuels are used in engines providing good performance and frequently operating with a high load, i.e. under conditions close to knocking, this type of fuel is expected to have a very good resistance to spontaneous combustion.

Moreover, for aviation fuel two characteristics are determined which are comparable to octane numbers: one, the MON or motor octane number, relating to operating with a slightly lean mixture (cruising power), the other, the Octane rating. Performance Number or PN, relating to use with a distinctly richer mixture (take-off). With the objective of guaranteeing high octane requirements, at the aviation fuel production stage, an organic lead compound, and more particularly tetraethyllead (TEL), is generally added. Without the TEL added, the MON is typically around 91. As noted above ASTM D910, 100 octane aviation fuel requires a minimum motor octane number (MON) of 99.6. The distillation profile of the high octane unleaded aviation fuel composition should have a T10 of maximum 75° C., T40 of minimum 75° C., T50 of maximum 105° C., and T90 of maximum 135° C.

As in the case of fuels for land vehicles, administrations are tending to lower the lead content, or even to ban this additive, due to it being harmful to health and the environment. Thus, the elimination of lead from the aviation fuel composition is becoming an objective.

Attempts have been made in the past to produce a high octane unleaded aviation fuel that meet most of the ASTM D910 specification for high octane aviation fuel. In addition to the MON of 99.6, it is also important to not negatively impact the flight range of the aircraft, vapor pressure, and freeze points that meets the aircraft engine start up requirements and continuous operation at high altitude.

U.S. Pat. Nos. 9,127,225, 9,388,359, 9,388,357, 9,388,358, 9,120,991, 9,388,356, 9,035,114 all relate to various unleaded aviation fuel compositions that meet most of the ASTM D910 specification for 100 octane aviation fuel.

U.S. Pat. No. 9,120,991 discloses unleaded aviation fuel compositions comprising toluene, toluidine, alkylate or alkylate blend, branched acetate and isopentane.

U.S. Pat. No. 9,388,356 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, branched chain alcohol and isopentane.

U.S. Pat. No. 9,388,357 discloses unleaded aviation fuel compositions comprising toluene, aromatic amine component comprising toluidine, alkylate or alkylate blend and isopentane.

U.S. Pat. No. 9,388,358 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, diethyl carbonate, and isopentane.

U.S. Pat. No. 9,388,359 discloses unleaded aviation fuel compositions comprising toluene, toluidine, alkylate or alkylate blend, diethyl carbonate and isopentane.

U.S. Pat. No. 9,035,114 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, branched alkyl acetate and isopentane.

U.S. Pat. No. 9,127,225 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, C4-C5 alcohol, and isopentane.

US2018/0305628 relates to aviation fuels comprising 56-88 wt % mesitylene and 10-20 wt % isopentane.

While the types of compositions disclosed in the above mentioned patent publications may meet most of the ASTM D910 specification for 100 octane aviation fuel, it has been found that some undesirable effects on bladder components within the aircraft can still occur. Bladder tanks are reinforced rubberized bags installed in a section of aircraft structure designed to accommodate fuel. Many high-performance light aircraft, helicopters and some smaller turboprop aircraft use bladder tanks. In particular, problems such as bladder shrinkage and delamination have been observed with types of compositions disclosed in the above mentioned prior art, for example, those disclosed in U.S. Pat. No. 9,035,114B1. As well as bladder shrinkage, said prior art compositions can exhibit materials compatability issues, such as elastomer swelling and paint staining, as well as engine endurance issues. It would therefore be desirable to formulate a high octane unleaded aviation fuel which serves to mitigate these problems while still meeting most of the requirements of the ASTM D910 specification.

It has surprisingly been found by the present inventors that the high octane unleaded aviation fuel composition of the present invention having reduced aromatics (aniline) content and a certain amount of mesitylene and C4/C5 isoparaffins prevents and/or reduces shrinkage and delamination of the bladder material, provides improved materials compatibility such as reduced elastomer swelling and reduced paint staining, and provides improved engine endurance, while still meeting most of the requirements of the ASTM D910 specification.

SUMMARY OF THE INVENTION

According to the present invention there is provided an unleaded aviation fuel composition having a MON of at least 99.6, sulfur content of less than 0.05 wt %, CHN content of at least 98 wt %, less than 2 wt % of oxygen content, an adjusted heat of combustion of at least 43.5 MJ/kg, a vapor pressure in the range of 38 to 49 kPa, comprising:

-   -   from 5 vol. % to 25 vol. % of toluene having a MON of at least         107;     -   from 0.5 vol. % to 4 vol. % of aniline;     -   from 30 vol % to 70 vol % of at least one alkylate or alkyate         blend having an initial boiling range of from 32° C. to 60° C.         and a final boiling range of from 105° C. to 140° C., having T40         of less than 99° C., T50 of less than 100° C., T90 of less than         110° C., the alkylate or alkylate blend comprising isoparaffins         from 4 to 9 carbon atoms, 3-20 vol % of C5 isoparaffins, 3-15         vol % of C7 isoparaffins, and 60-90 vol % of C8 isoparaffins,         based on the alkylate or alkylate blend, and less than 1 vol %         of C10+, based on the alkylate or alkylate blend;     -   from 0.1 vol. % to 8 vol. % of branched alkyl acetate;     -   at least 8 vol % of isopentane, isobutane, or mixture thereof in         an amount sufficient to reach a vapor pressure in the range of         38 to 49 kPa;     -   from 2 vol. % to 10 vol. % of mesitylene;     -   wherein the fuel composition contains less than 1 vol % of C8         aromatics.

The features and advantages of the invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate certain aspects of some of the embodiments of the invention, and should not be used to limit or define the invention.

FIG. 1 is a photograph which shows the appearance of a bladder sample which has not been exposed to any fuel.

FIG. 2 is a photograph which shows the appearance of a bladder sample after it has been soaked in Reference Fuel A for 123 hours at 135° F. as described in the Bladder Testing Examples below.

FIG. 3 is a photograph which shows the appearance of an bladder sample after it has been soaked in the fuel of Example 1 for 123 hours at 135° F. as described in the Bladder Testing Examples below.

FIG. 4 is a graphical representation of the data set out in Table 4 (where the elastomer material tested is nitrile rubber).

FIG. 5 is a graphical representation of the data set out in Table 4 (where the elastomer material tested is fluorosilicone).

FIG. 6 is a graphical representation of the data set out in Table 4 (where the elastomer material tested is fluorocarbon).

FIG. 7 is a graphical representation of the data set out in Table 10 (where the sealant material is AC-350B)

FIG. 8 is a graphical representation of the data set out in Table 11 (where the sealant material is PR1440-B)

FIG. 9 is a graphical representation of the data set out in Table 12 (where the sealant material is CS3204-B)

DETAILED DESCRIPTION OF THE INVENTION

We have found that a high octane unleaded aviation fuel having the formulation disclosed herein meets most of the ASTM D910 specification for 100 octane aviation fuel while also reducing or preventing bladder delamination, providing acceptable materials compatibility properties such as reduced elastomer swelling and reduced paint staining, as well as providing improved engine endurance properties. The unleaded aviation fuel composition of the present invention can be produced by a blend comprising from about 5 vol % to about 25 vol % of high MON toluene, from about 0.5 vol % to about 4 vol % of aniline, from about 30 vol % to about 70 vol % of at least one alkylate cut or alkylate blend that have certain composition and properties, at least 8 vol % of isopentane, isobutane or a mixture thereof and from about 2 vol. % to less than 10 vol. % of mesitylene. The high octane unleaded aviation fuel of the invention has a MON of greater than 99.6.

Further the unleaded aviation fuel composition contains less than 1 vol %, preferably less than 0.5 vol % of C8 aromatics. It has been found that C8 aromatics such as xylene may have materials compatibility issues, particularly in older aircraft. Further it has been found that unleaded aviation fuel containing C8 aromatics tend to have difficulties meeting the temperature profile (ASTM D86) of D910 specification.

In another embodiment, the unleaded aviation fuel contains no noncyclic ethers. In another embodiment, the unleaded aviation fuel contains no alcohol boiling less than 80° C. Further, the unleaded aviation fuel composition has a benzene content between 0% v and 5% v, preferably less than 1% v.

Further, in some embodiments, the volume change of the unleaded aviation fuel tested for water reaction is within +/−2 mL as defined in ASTM D1094.

The high octane unleaded fuel will not contain lead and preferably not contain any other metallic octane boosting lead equivalents. The term “unleaded” is understood to contain less than 0.01 g/L of lead. The high octane unleaded aviation fuel will have a sulfur content of less than 0.05 wt %. In some embodiments, it is preferred to have ash content of less than 0.0132 g/L (0.05 g/gallon) (ASTM D-482).

According to current ASTM D910 specification, the NHC should be close to or above 43.5 mJ/kg. The Net Heat of Combustion value is based on a current low density aviation fuel and does not accurately measure the flight range for higher density aviation fuel. It has been found that for unleaded aviation gasolines that exhibit high densities, the heat of combustion may be adjusted for the higher density of the fuel to more accurately predict the flight range of an aircraft.

There are currently three approved ASTM test methods for the determination of the heat of combustion within the ASTM D910 specification. Only the ASTM D4809 method results in an actual determination of this value through combusting the fuel. The other methods (ASTM D4529 and ASTM D3338) are calculations using values from other physical properties. These methods have all been deemed equivalent within the ASTM D910 specification.

Currently the Net Heat of Combustion for Aviation Fuels (or Specific Energy) is expressed gravimetrically as MJ/kg. Current lead containing aviation gasolines have a relatively low density compared to many alternative unleaded formulations. Fuels of higher density have a lower gravimetric energy content but a higher volumetric energy content (MJ/L).

The higher volumetric energy content allows greater energy to be stored in a fixed volume. Space can be limited in general aviation aircraft and those that have limited fuel tank capacity, or prefer to fly with full tanks, can therefore achieve greater flight range. However, the more dense the fuel, then the greater the increase in weight of fuel carried. This could result in a potential offset of the non-fuel payload of the aircraft. Whilst the relationship of these variables is complex, the formulations in this embodiment have been designed to best meet the requirements of aviation gasoline. Since in part density effects aircraft range, it has been found that a more accurate aircraft range, normally gauged using Heat of Combustion, can be predicted by adjusting for the density of the avgas using the following equation:

HOC*=(HOCv/density)+(% range increase/% payload increase+1)

where HOC* is the adjusted Heat of Combustion (MJ/kg), HOCv is the volumetric energy density (MJ/L) obtained from actual Heat of Combustion measurement, density is the fuel density (g/L), % range increase is the percentage increase in aircraft range compared to 100 LL(HOCLL) calculated using HOCv and HOCLL for a fixed fuel volume, and % payload increase is the corresponding percentage increase in payload capacity due to the mass of the fuel.

The adjusted heat of combustion will be at least 43.5 MJ/kg, and have a vapor pressure in the range of 38 to 49 kPa. The high octane unleaded fuel composition will further have a freezing point of −58° C. or less. Unlike for automobile fuels, for aviation fuel, due to the altitude while the plane is in flight, it is important that the fuel does not cause freezing issues in the air.

Further, the final boiling point of the high octane unleaded fuel composition should be less than 190° C., preferably at most 180° C. measured with greater than 98.5% recovery as measured using ASTM D-86. If the recovery level is low, the final boiling point may not be effectively measured for the composition (i.e., higher boiling residual still remaining rather than being measured). The high octane unleaded aviation fuel composition of the invention have a Carbon, Hydrogen, and Nitrogen content (CHN content) of at least 98 wt %, preferably 99 wt %, (and less than 2 wt %, preferably 1 wt % or less of oxygen-content.

Suitably, the unleaded aviation fuel composition of the present invention has an aromatics content measured according to ASTM D5134 of greater than 15 vol % to about 35 vol %, preferably in the range of 20 vol % to about 35 vol %, more preferably in the range from 20 vol % to 30 vol %, by weight of the total unleaded aviation fuel composition.

It has been found that the high octane unleaded aviation fuel of the invention not only meets the MON value for 100 octane aviation fuel, but also meets the vapor pressure, adjusted heat of combustion, and freezing point. In addition to MON it is important to meet the vapor pressure, temperature profile, and minimum adjusted heat of combustion for aircraft engine start up and smooth operation of the plane at higher altitude. Preferably the potential gum value is less than 6 mg/100 mL. In some embodiments, the high octane unleaded aviation fuel has T10 of at most 80° C., a T40 of at least 75° C., a T50 of at most 105° C., a T90 of at most 135° C. and a final boiling point of less than 190° C.

It is difficult to meet the demanding specification for unleaded high octane aviation fuel while also having acceptable materials compatibility, elastomer swelling, bladder delamination, paint staining and engine endurance properties. It has been found that the unleaded aviation fuel composition of the present invention comprising a certain blend of components in certain amounts serves to address these problems.

Toluene

Toluene occurs naturally at low levels in crude oil and is usually produced in the processes of making gasoline via a catalytic reformer, in an ethylene cracker or making coke from coal. Final separation, either via distillation or solvent extraction, takes place in one of the many available processes for extraction of the BTX aromatics (benzene, toluene and xylene isomers). The toluene used in the invention must be a grade of toluene that have a MON of at least 107 and containing less than 1 vol % of C8 aromatics. Further, the toluene component preferably has a benzene content between 0% v and 5% v, preferably less than 1% v.

Toluene is preferably present in the blend in an amount from about 5% v, preferably at least about 10% v, most preferably at least about 15% v to at most about 25% v, preferably to at most about 23% v, more preferably to at most about 20% v, based on the unleaded aviation fuel composition.

Aniline

Aniline (C₆H₅NH₂) is mainly produced in industry in two steps from benzene. First, benzene is nitrated using a concentrated mixture of nitric acid and sulfuric acid at 50 to 60° C., which gives nitrobenzene. In the second step, the nitrobenzene is hydrogenated, typically at 200-300° C. in presence of various metal catalysts.

As an alternative, aniline is also prepared from phenol and ammonia, the phenol being derived from the cumene process.

In commerce, three brands of aniline are distinguished: aniline oil for blue, which is pure aniline; aniline oil for red, a mixture of equimolecular quantities of aniline and ortho- and para-toluidines; and aniline oil for safranine, which contains aniline and ortho-toluidine, and is obtained from the distillate (échappés) of the fuchsine fusion. Pure aniline, otherwise known as aniline oil for blue is desired for high octane unleaded avgas. Aniline is preferably present in the blend in an amount from about 0.5% v, preferably at least about 1% v, most preferably at least about 1.5% v to at most about 4% v, preferably to at most about 3% v, more preferably to at most about 2% v, based on the unleaded aviation fuel composition.

Alkylate and Alkyate Blend

The term alkylate typically refers to branched-chain paraffin. The branched-chain paraffin typically is derived from the reaction of isoparaffin with olefin. Various grades of branched chain isoparaffins and mixtures are available. The grade is identified by the range of the number of carbon atoms per molecule, the average molecular weight of the molecules, and the boiling point range of the alkylate. It has been found that a certain cut of alkylate stream and its blend with isoparaffins such as isooctane is desirable to obtain or provide the high octane unleaded aviation fuel of the invention. These alkylate or alkylate blend can be obtained by distilling or taking a cut of standard alkylates available in the industry. It is optionally blended with isooctane. In a preferred embodiment herein, alkylate/alkylate blend is blended with isooctane. The alkylate or alkyate blend have an initial boiling range of from about 32° C. to about 60° C. and a final boiling range of from about 105° C. to about 140° C., preferably to about 138° C., more preferably to about 137° C., having T40 of less than 99° C., T50 of less than 100° C., T90 of less than 110° C., preferably at most 108° C., the alkylate or alkylate blend comprising isoparaffins from 4 to 9 carbon atoms, about 3-20 vol % of C5 isoparaffins, based on the alkylate or alkylate blend, about 3-15 vol % of C7 isoparaffins, based on the alkylate or alkylate blend, and about 60-90 vol % of C8 isoparaffins, based on the alkylate or alkylate blend, and less than 1 vol % of C10+, preferably less than 0.1 vol %, based on the alkylate or alkylate blend; Alkylate or alkylate blend is preferably present in the unleaded aviation fuel composition in an amount from about 30% v, preferably at least about 35% v, most preferably at least about 40% v to at most about 70% v, preferably to at most about 65% v, more preferably to at most about 60% v.

Isopentane/Isobutane

Isopentane, isobutane or a mixture thereof is present in an amount of at least 8 vol % in an amount sufficient to reach a vapor pressure in the range of 38 to 49 kPa. The alkylate or alkylate blend also contains C5 isoparaffins so this amount will typically vary between 8 vol % and 25 vol % depending on the C4/C5 content of the alkylate or alkylate blend. Isopentane and/or isobutane should be present in an amount to reach a vapor pressure in the range of 38 to 49 kPa to meet aviation standard. The total isopentane and/or isobutane content in the unleaded aviation fuel composition is typically in the range of 10 vol % to 20 vol %, preferably in the range of 10% to 15% by volume, based on the aviation fuel composition.

There is a tendency for isopentane to reduce the MON and increase the RVP, while there is a tendency for isobutane to increase the MON and increase the RVP. It has been found that if there is too much of either isopentane or isobutane then the RVP is too high. Hence, in a preferred embodiment, the volume ratio of isopentane to isobutane is at least 2:1, preferably at least 2.5:1, more preferably at least 3:1, and at most 4:1, preferably at most 3.5:1, more preferably at most 3.3:1.

Alkyl Acetate

The unleaded aviation fuel may contain a branched alkyl acetate having branched chain alkyl group having 4 to 8 carbon atoms as a co-solvent. Suitable co-solvent may be, for example, t-butyl acetate, iso-butyl acetate, ethylhexylacetate, iso-amyl acetate, and t-butyl amyl acetate, or mixtures thereof. It has been found that branched chain alkyl acetates having an alkyl group of 4 to 8 carbon atoms dramatically decrease the freezing point of the unleaded aviation fuel to meet the current ASTM D910 standard for aviation fuel. The branched acetate is present in an amount from 0.1 vol %, to 10 vol %, preferably from 1 vol % to 8 vol %, more preferably from 2 vol % to 6 vol %, even more preferably from 4 vol % to 6 vol %, based on the unleaded aviation fuel composition. A preferred branched alkyl acetate for use herein is t-butyl acetate.

The branched alkyl acetate is useful for ensuring that the aniline remains in solution. In a preferred embodiment herein, the volume ratio of the branched alkyl acetate to aniline is at least 1.5:1, preferably at least 2:1, more preferably at least 2.5:1, and at most 4:1, preferably at most 3.5:1, more preferably at most 3:1.

Preferably the water reaction volume change is within +/−2 ml for aviation fuel. Water reaction volume change is large for ethanol that makes ethanol not suitable for aviation gasoline.

Mesitylene

Another essential component of the unleaded aviation fuel composition herein is mesitylene (1,3,5-trimethylbenzene). Mesitylene is present in the unleaded aviation fuel composition at a level of from 2 vol. % to 10 vol. %, preferably from 3 vol % to 8 vol. %, more preferably from 5 vol. % to 7 vol. %, based on the unleaded aviation fuel composition. The ranges of mesitylene given above are specifically selected to provide the desired properties in the final unleaded aviation gasoline formulation. If too high an amount of mesitylene is used the final density of the unleaded aviation fuel composition is too high and there can be issues with starting the engine and sooting.

In a preferred embodiment herein, the total amount of mesitylene and toluene should not exceed 25 vol %. If the total amount of aromatic components in the final fuel composition is too high, this can lead to issues with materials compatibility with bladder material.

Blending

For the preparation of the high octane unleaded aviation gasoline, the blending can be in any order as long as they are mixed sufficiently. It is preferable to blend the toluene, mesitylene and alkylate blend together, followed by the isopentane, isobutane, and then the t-butyl acetate and the aniline (in that order) and to mix the blend for about 2 hours. This order of addition helps to prevent the aniline dropping out of solution.

In order to satisfy other requirements, the unleaded aviation fuel according to the invention may contain one or more additives which a person skilled in the art may choose to add from standard additives used in aviation fuel. There should be mentioned, but in non-limiting manner, additives such as antioxidants, anti-icing agents, antistatic additives, corrosion inhibitors, dyes and their mixtures.

According to another embodiment of the present invention a method for operating an aircraft engine, and/or an aircraft which is driven by such an engine is provided, which method involves introducing into a combustion region of the engine and the high octane unleaded aviation gasoline fuel formulation described herein. The aircraft engine is suitably a spark ignition piston-driven engine. A piston-driven aircraft engine may for example be of the inline, rotary, V-type, radial or horizontally-opposed type.

The unleaded aviation gasoline fuel formulation described herein provides improvements in materials compatibility, reduced elastomer swelling, reduced paint staining, improved engine endurance and reduced bladder shrinkage or delamination. Hence, according to another embodiment of the present invention there is provided a use of an unleaded aviation fuel composition having a MON of at least 99.6, sulfur content of less than 0.05 wt %, CHN content of at least 98 wt %, less than 2 wt % of oxygen content, an adjusted heat of combustion of at least 43.5 MJ/kg, a vapor pressure in the range of 38 to 49 kPa, comprising a blend comprising:

-   -   from 5 vol. % to 25 vol. % of toluene having a MON of at least         107;     -   from 0.5 vol. % to 4 vol. % of aniline;     -   from 30 vol % to 70 vol % of at least one alkylate or alkyate         blend having an initial boiling range of from 32° C. to 60° C.         and a final boiling range of from 105° C. to 140° C., having T40         of less than 99° C., T50 of less than 100° C., T90 of less than         110° C., the alkylate or alkylate blend comprising isoparaffins         from 4 to 9 carbon atoms, 3-20 vol % of C5 isoparaffins, 3-15         vol % of C7 isoparaffins, and 60-90 vol % of C8 isoparaffins,         based on the alkylate or alkylate blend, and less than 1 vol %         of C10+, based on the alkylate or alkylate blend;     -   from 0.1 vol. % to 10 vol. % of branched alkyl acetate;     -   at least 8 vol % of isopentane, isobutane, or mixture thereof in         an amount sufficient to reach a vapor pressure in the range of         38 to 49 kPa;     -   from 2 vol. % to 10 vol. % of mesitylene;     -   wherein the fuel composition contains less than 1 vol % of C8         aromatics for the purpose of providing one or more of:     -   (i) improved materials compatibility     -   (ii) reduced elastomer swelling     -   (iii) reduced paint staining     -   (iv) improved engine endurance     -   (v) reduced bladder delamination.

As used herein, the term ‘materials compatability’ means the effect of the fuel on a material, such as bladder, paint, elastomers, sealants (such as polysulfide), and the like. In the context of this aspect of the invention, the term ‘improved materials compatibility’ embraces any degree of improvement in materials compatibility. The improvement in materials compatibility may be of the order of 10% or more, preferably 20% or more, more preferably 50% or more, and especially 70% or more compared to the materials compatibility exhibited by an analogous fuel formulation which does not contain the same blend of components in the specified amounts as the fuel formulations of the present invention, such as, for example, the fuel formulations exemplified in U.S. Pat. No. 9,035,114B1.

As used herein, the term ‘elastomer swelling’ means the swelling effect of the fuel on an elastomer material. Elastomer swelling can be measured by any suitable test method, such as that reported in ‘Final Report for Alternative Fuels Task: Impact of SPK Fuels and Fuel Blends on Non-metallic Materials used in Commercial Aircraft Fuel Systems’ dated 29 Jul. 2011, updated 18 Dec. 2013, authors: John L. Graham (University of Dayton Research Institute. Further, in the context of this aspect of the invention, the term ‘reduced elastomer swelling’ embraces any degree of reduction in elastomer swelling. The reduction in elastomer swelling may be of the order of 10% or more, preferably 20% or more, more preferably 50% or more, and especially 70% or more compared to the materials compatibility exhibited by an analogous fuel formulation which does not contain the same blend of components in the specified amounts as the fuel formulations of the present invention.

As used herein, the term ‘paint staining’ means the staining effect that the fuel has on a paint, such as the paint used to coat the outside of an aircraft. It is undesirable for the end user for the paint to be stained every time it comes into contact with the fuel. Paint staining can be measured by any suitable test method, such as ATSM D2244-16 (Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Colour Coordinates). In the context of this aspect of the invention, the term ‘reduced paint staining’ embraces any degree of reduction in paint staining. The reduction in paint staining may be of the order of 10% or more, preferably 20% or more, more preferably 50% or more, and especially 70% or more compared to the paint staining exhibited by an analogous fuel formulation which does not contain the same blend of components in the specified amounts as the fuel formulations of the present invention.

As used herein, the term ‘engine endurance’ means the engine performance over an extended period of time, e.g. 500 hours or more. A suitable test method for measuring engine endurance is disclosed in PAFI-ETP-009 Rev F; PAFI Phase II Durability & Performance Tests (Continental Model TSIO-550-K Engine) dated 14 Mar. 2019. Further in the context of this aspect of the invention, the term ‘improved engine endurance’ embraces any degree of improvement in engine endurance. The improvement in engine endurance may be of the order of 10% or more, preferably 20% or more, more preferably 50% or more, and especially 70% or more compared to the engine endurance exhibited by an analogous fuel formulation which does not contain the same blend of components in the specified amounts as the fuel formulations of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of examples herein described in detail. It should be understood, that the detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. The present invention will be illustrated by the following illustrative embodiment, which is provided for illustration only and is not to be construed as limiting the claimed invention in any way.

EXAMPLES Test Methods

The following test methods were used for the measurement of the aviation fuels.

-   -   Motor Octane Number: ASTM D2700     -   Tetraethyl Lead Content: ASTM D5059     -   Density: ASTM D4052     -   Distillation: ASTM D86     -   Vapor Pressure: ASTM D323     -   Freezing Point: ASTM D2386     -   Sulfur: ASTM D2622     -   Net Heat of Combustion (NHC): ASTM D3338     -   Copper Corrosion: ASTM D130     -   Oxidation Stability—Potential Gum: ASTM D873     -   Oxidation Stability—Lead Precipitate: ASTM D873     -   Water Reaction—Volume change: ASTM D1094     -   Detail Hydrocarbon Analysis (ASTM 5134)

Example 1

An aviation fuel composition of the invention was blended as follows. The toluene (107 MON), mesitylene and alkylate blend were mixed together, followed by the isopentane, isobutane, and then the t-butyl acetate followed by the aniline (in that order) and the blend was mixed for about 2 hours. The alkylate blend had the properties shown in Table 1 below.

TABLE 1 Narrow Cut Alkylate Blend Properties IBP (ASTM D86, ° C.) 50 FBP (ASTM D86, ° C.) 136.2 T40 (ASTM D86, ° C.) 98.7 T50 (ASTM D86, ° C.) 99.8 T90 (ASTM D86, ° C.) 106.7 Vol % iso-C5 5.91 Vol % iso-C7 7.60 Vol % iso-C8 79.375 Vol % C10+ <1

Example 1

Light alkylate blend 55% v  Toluene 19% v  Isopentane 10% v  Isobutane 3% v Mesitylene 6% v Aniline 2% v t-butyl acetate 5% v

The physical properties of Example 1 are shown in the table below:

Property D910 Spec Example 1 MON 99.6 (min) 100.3 RVP (kPa) 38 (min)/49 (max)  45.7 Freeze Point (deg C.) −58 (max) <−65   Density (kg/m³) Report kg/m3 746   Net Heat of Combustion 43.5 (min)   42.236 (MJ/kg) Adjusted Net Heat of N/A  43.5 Combustion (MJ/kg) Water Reaction (mL) +/−2 (max)  0 T10 (deg C.) 75 (max)  77.7 T40 (deg C.) 75 (min) 100.3 T50 (deg C.) 105 (max) 101.8 T90 (deg C.) 135 (max) 128.3 FBP (deg C.) 170 (max) 162   Copper Corrosion 1 (max)   1a Oxidization Stability 6 (max) <1  (mg/100 ml) Electrical Conductivity 500 (max) 18  (pS/m)

Reference Example A

Reference Example A contained the same grades of light alkylate blend, toluene, isopentane, aniline and t-butyl acetate as Example 1. However, Reference Example A did not contain any isobutane or mesitylene and contained higher amounts of aniline than in Example 1.

Reference Example A was prepared as follows. Toluene having 107 MON was blended with Aniline while mixing. Narrow Cut Alkylate having the properties shown in Table 1 above were poured into the mixture. Then, t-butyl acetate was added, followed by isopentane to complete the blend.

Fuels having similar composition and characteristics to Reference Example A are disclosed in U.S. Pat. No. 9,035,114B1.

Light alkylate Blend 40.5% v Toluene 30% v Isopentane 15% v Isobutane 0% v Mesitylene 0% v Aniline 4.5% v t-butyl acetate 10% v

The physical properties of Reference Example A are shown in the table below:

Property D910 Spec MON 99.6 (min) 100   RVP (kPa) 38 (min)/49 (max) 43  Freeze Point (deg C.) −58 (max) −65  Density (g/mL) Report kg/m3 770   Net Heat of Combustion 43.5 (min)  40.8 (kg/m3) Adjusted Net Heat of N/A  42.0 Combustion (MJ/ kg) Water Reaction (units) +/−2 (max)  0.5 T10 (deg C.) 75 (max)  67.2 T40 (deg C.) 75 (min) 100.6 T50 (deg C.) 105 (max) 103.1 T90 (deg C.) 135 (max) 114.8 FBP (deg C.) 170 (max) 183.7 Copper Corrosion 1 (max)   1a Oxidization Stability 6 (max)  1 (mg/100 ml) Electrical Conductivity 500 (max) 359   (pS/m)

Density/Sooting

The fuel of Example 1 is much less dense than the fuel of Reference Example A and therefore exhibits less sooting and improved engine performance.

Bladder Testing

In order to measure the effect of fuel on a bladder, the following experiments were carried out. The fuels assessed in these experiments were Example 1, Reference Example 1 and a commercially available 100LL Avgas fuel. A bladder coupon was soaked in fuel for 123 hours at 130° F. Roughness and waviness values of the new bladder (at the start of the test) and the bladder after being soaked in fuel for 123 days were measured using an NPFLEX® instrument. This instrument provided 3D non-contact measurements of the surface feature. The results are shown in the Table below.

TABLE 2 Average Average Roughness (μm) Waviness (μm) New Bladder 0.61 6.52 Bladder with 1.43 7.79 Example 1 Bladder with 100LL 1.58 11.98 Bladder with Ref. 2.96 19.24 Ex. A

As can be seen in Table 2, the bladder which has been soaked in the fuel of the present invention (Example 1) exhibited reduced roughness and reduced waviness values compared to the bladder which had been soaked in the fuel of Reference Example A and the commercially available 100LL fuel.

FIG. 1 is a photograph which shows the appearance of a bladder sample which has not been exposed to any fuel.

FIG. 2 is a photograph which shows the appearance of a bladder sample after it has been soaked in Reference Fuel A for 123 hours at 135° F.

FIG. 3 is a photograph which shows the appearance of an bladder sample after it has been soaked in the fuel of Example 1 for 123 hours at 135° F.

As can be seen from FIGS. 1-3 , when compared to the appearance of the new bladder, the bladder which was soaked in Reference Example A appears to be much more wrinkled in appearance than the bladder which was soaked in Example 1 (according to the present invention).

These experiments demonstrate that the fuel of the present invention (Example 1) prevents delamination of the bladder compared to the reference fuel (Reference Example A).

Paint Panel Testing

In order to measure the effect of fuel on paint staining, the following experiment was carried out using standard test method ATSM D2244-16 (Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Colour Coordinates). Samples of paint panels were exposed to the fuel samples by dropping a few drops of fuel onto the panels and the panels are exposed to natural light for a couple of hours. The samples were aluminum panels measuring 8 inches×8 inches. The aluminium panels were coated with Jet Glo® Express Polyester Urethane which is a commercially available topcoat for use on aircraft and qualified to the SAE AMS 3095 specification for commercial airlines. The fuel samples used in this experiment were the fuel of Example 1 and the fuel of Reference Example A. After exposing the samples to fuel, the lightness of the samples were measured using a GRETAG MACBETH Color i5 spectrophotometer. The spectrophotometer exposes the surface of the sample to a light source and measures the reflected light using a 10° observer. Measurements were taken from the centre of the fuel exposed area of the sample. The values of L* (lightness), a* (red/green coordinate) and b* (yellow/blue coordinate) are reported in Table 3 below. The colour difference (delta) (compared to a control sample, i.e. a paint panel which was not exposed to fuel) was calculated and is reported as DE*2000 in Table 3 below.

TABLE 3 L* a * b* DE*2000 Control 88.75 −1.02 1.31 N/A sample Reference 87.93 −0.8  4.13 2.57 Fuel A Example 1 88.66 −0.97 2.24 0.87

As can be seen from the data in Table 3, the colour difference from the control sample was much smaller in the case of the fuel of Example 1 compared with Reference Fuel A. This means that the fuel of the present invention (Example 1) exhibited reduced paint staining compared with the reference fuel (Reference Fuel A).

Elastomer Swelling Tests

In order to measure the effect of fuel on elastomer swelling, the following experiment was carried out. Three types of test materials were used in the elastomer swelling experiments in the form of O-rings: nitrile rubber, fluorosilicone and fluorocarbon. The test samples were sectioned from these test materials. The fuel samples used in the elastomer swelling experiments were a commercially available 100LL aviation gasoline, a commercially available high aromatic 100LL gasoline, the fuel of Example 1 and the fuel of the Reference Example A. The volume swell of each material was measured by optical dilatometry at room temperature. Two samples of each material measuring approximately 2 mm×2 mm×1 mm were placed in an optical cell with 5 mL of fuel. Starting at 1 minute after being immersed in the fuel the samples were digitally photographed every 20 seconds for the next 3 minutes. At 5 minutes total elapsed time, the samples were photographed every 10 minutes until observed to be at equilibrium. After the aging period was complete, the cross sectional area was extracted from the digital images and taken as characteristic dimension proportional to the volume. The final volume swell was taken as the average of the two samples. The equilibrium volume swell of each material in each of the test fuels is summarized in Table 4 below.

FIGS. 3-5 are graphical representations of the data shown in Table 4. FIG. 3 is a graphical representation of the data shown in Table 4 where the material is nitrile rubber. FIG. 4 is a graphical representation of the data shown in Table 4 wherein the material is fluorosilicone. FIG. 5 is a graphical representation of the data shown in Table 4 where the material is fluorocarbon. Note that the bimodal behavior of the volume swell of the nitrile rubber O-ring material is typical. The initial rapid volume swell occurs during the paid absorption of fuel, while the gradual volume loss occurs as the fuel slowly extracts plasticizers and therefore show only volume swell as a function of time.

TABLE 4 Material Fuel Volume Swell Nitrile 100LL  8.35% Rubber High Aromatic 100LL 14.62% Reference Fuel A 50.48% Example 1 25.81% Fluoro- 100LL 13.68% silicone High Aromatic 100LL 15.16% Reference Fuel A 26.43% Example 1 19.98% Fluoro- 100LL  4.06% carbon High Aromatic 100LL  5.80% Reference Fuel A 32.06% Example 1 17.14%

The results shown in Table 4 and FIG. 3-5 demonstrate that the fuel of Example 1 (according to the present invention) significantly reduced the elastomer swelling for all materials compared with the reference fuel (Reference Fuel A). In particular, in the case of nitrile rubber, the fuel of Example 1 exhibited about 50% reduction of elastomer swelling compared with the reference fuel (Reference Fuel A).

Sealant Testing

In order to measure the effect of fuel on aerospace sealants, the following experiment was carried out. Various sealants were aged for 28 days and 70 days in the test fuels and then tests were performed on the aged sealants to measure Durometer A hardness, volume swell, peel strength and tensile strength and elongation. The fuels used in these tests were the fuel of Example 1 and a commercially available 100LL aviation fuel. The sealants used in the test were aerospace sealants qualified to AMS-S-8802 Types 1 and 2, AMS3276, AMS3277 and AMS3281.

Specimens for hardness, volume swell and tensile strength and elongation testing were prepared from flowsheets by injecting the sealant into a 12″×12″ mold consisting of two exterior metal places, two interior Teflon sheets and a Teflon spacer to ensure a uniform flow sheet with a thickness of 0.125 inches. Once the sealant was injected, the material was cured in the closed mold until the material reaches stadarad cure, per the applicable material specification. The material was then removed from the mold and cures open-faced in an environmentally controlled chamber at standard conditions until the full cure time was reached. Upon completion of cure, the specimens were prepared for fuel exposure. The specimens were prepared, cut and initial measurements recorded and then put into glass jars filled with test fuel, placed in the oven and aged for 28 days or 70 days in the test fuels.

The hardness, volume swell and tensile strength/elongation testing was performed in accordance with established ASTM procedures as listed below:

-   -   Durometer A hardness: ASTM D2240     -   Volume swell: ASTM D471     -   Tensile strength and elongation: ASTM D412

Specimens for peel strength were prepared in accordance with AS512/1C on panels coated with AMS-C-27725 polyurethance for aircraft integral fuel tanks. The sealant was was applied to stainless steel mesh screens using a metal spatula to ensure the sealant was worked into the pulling medium, saturating approx. 5 inches of the screen. Next the pulling medium was joined to the sealing compound on the coated panel. The panel and screen were coated with approx. 0.125 inches of sealant. After the screen was added to the panel, an additional layer of sealant of approx. 0.030 inches was applied to the panel to complete the peel strength sample assembly. The panels were cured at standard conditions for the cure times designated in each material specification. The panels were aged in the test fuels for 28 days or 70 days. After aging, the panels were removed from the fluid and the stainless steel mesh was cut on all sides the entire length of the panel. Once the pulling medium has been cut, the specimen was clamped in an Instron at 180 degrees from the top of the panel. The specimen was pulled apart from the pulling medium as the clamps moved at a separation rate of 2 inches per minute. An initial cut at a 45 degree angle was made through the sealing compound and down to the panel substrate. The pulling medium continued to pull apart from the panel with cuts made every one inch. This was repeated for a minimum of three times. After testing, the average peak loads from the Instron software were recorded and the panel was examined for percentage of cohesive failure.

The test results are shown in Tables 5-8 below. All specimens were made in replicates of five and the average reported.

TABLE 5 (Tensile Strength) 100LL Fuel of Fuel Example 1 Tensile Tensile Sealant Conditioning Strength Strength PR 1422 B-2 28 days at 335.1 265.3 SAE-AMS-S-8802 140° F. Type 1 Class 70 days at 326 233 B-2 140° F. PR 1440 B-2 28 days at 430.1 313.6 SAE-AMS-S-8802 140° F. Type 2 Class 70 days at 364.8 264.2 B-2 140° F. PR 1750 B-2 28 days at 410.4 302.5 SAE-AMS3276 140° F. Class B-2 70 days at 385.1 277.2 140° F. PR 2001 B-2 28 days at 244.9 244.4 SAE-AMS3277 140° F. Type 2 Class 70 days at 227 222 B-2 140° F. AC 370 B-2 28 days at 209.1 146 SAE-AMS-3281 140° F. Type 1 Class 70 days at 227 138.6 B-1/2 140° F. CS 3204 28 days at 317 psi 225.3 psi   Class A-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F. CS 3204 28 days at 247 psi 175 psi Class B-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F.

TABLE 6 (Elongation) 100LL Exam- Fuel ple 1 Sealant Conditioning % Elongation % Elongation PR 1422 B-2 28 days at 312 350.09 SAE-AMS-S-8802 140° F. Type 1 Class 70 days at 292 401 B-2 140° F. PR 1440 B-2 28 days at 211 363.15 SAE-AMS-S-8802 140° F. Type 2 Class 70 days at 206 441.51 B-2 140° F. PR 1750 B-2 28 days at 193 336.57 SAE-AMS3276 140° F. Class B-2 70 days at 191 414.04 140° F. PR 2001 B-2 28 days at 266 302.11 SAE-AMS3277 140° F. Type 2 Class 70 days at 256 413 B-2 140° F. AC 370 B-2 28 days at 282 359.62 SAE-AMS-3281 140° F. Type 1 Class 70 days at 256 519 B-1/2 140° F. CS 3204 28 days at 297% 439% Class A-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F. CS 3204 28 days at 286% 467% Class B-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F.

TABLE 7 (peel strength) 100LL Example 1 Peel Peel Sealant Conditioning Strength Strength PR 1422 B-2 28 days at 59.6 lbs/ 55.7 lbs/ SAE-AMS-S-8802 140° F. 100% 100% Type 1 Class 70 days at 50 lbs/ 58 lbs/ B-2 140° F. 100% 100% PR 1440 B-2 28 days at 35.8 lbs/ 39 lbs/ SAE-AMS-S-8802 140° F. 100% 100% Type 2 Class 70 days at 34.4 lbs/ 40.2 lbs/ B-2 140° F. 100% 100% PR 1750 B-2 28 days at 41.8 lbs/ 44 lbs/ SAE-AMS3276 140° F. 100% 100% Class B-2 70 days at 34.0 lbs/ 44 lbs/ 140° F. 100% 100% PR 2001 B-2 28 days at 65.2 lbs/ 49 lbs/ SAE-AMS3277 140° F. 100% 100% Type 2 Class 70 days at 55 lbs/ 50 lbs/ B-2 140° F. 100% 100% AC 370 B-2 28 days at 36.6 lbs/ 35.9 lbs/ SAE-AMS-3281 140° F. 100% 100% Type 1 Class 70 days at 32.2 lbs/ 43.4 lbs/ B-1/2 140° F. 100% 100% CS 3204 28 days at 31 lbs/ 28 lbs/ Class A-2 140° F. 100% 100% SAE-AMS-S-8802 70 days at Type 2 140° F. CS 3204 28 days at 43 lbs/ 44 lbs/ Class B-2 140° F. 100% 100% SAE-AMS-S-8802 70 days at Type 2 140° F.

TABLE 8 (volume swell) 100LL Example 1 % Volume % Volume Sealant Conditioning Swell Swell PR 1422 B-2 28 days at 9% 22% SAE-AMS-S-8802 140° F. Type 1 Class 70 days at 8% 21% B-2 140° F. PR 1440 B-2 28 days at 5% 18% SAE-AMS-S-8802 140° F. Type 2 Class 70 days at 4% 18% B-2 140° F. PR 1750 B-2 28 days at 4% 18% SAE-AMS3276 140° F. Class B-2 70 days at 5% 18% 140° F. PR 2001 B-2 28 days at 11%  28% SAE-AMS3277 140° F. Type 2 Class 70 days at 10%  30% B-2 140° F. AC 370 B-2 28 days at 2% 13   SAE-AMS-3281 140° F. Type 1 Class 70 days at 1% 13.3 B-1/2 140° F. CS 3204 28 days at 1%   13.5% Class A-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F. CS 3204 28 days at 6%   20.3% Class B-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F.

TABLE 9 (hardness) 100LL Example 1 Sealant Conditioning Hardness Hardness PR 1422 B-2 28 days at 59 43 SAE-AMS-S-8802 140° F. Type 1 Class 70 days at 56 39 B-2 140° F. PR 1440 B-2 28 days at 54 32.6 SAE-AMS-S-8802 140° F. Type 2 Class 70 days at 52 28.9 B-2 140° F. PR 1750 B-2 28 days at 55 33.3 SAE-AMS3276 140° F. Class B-2 70 days at 55 31.3 140° F. PR 2001 B-2 28 days at 43 29 SAE-AMS3277 140° F. Type 2 Class 70 days at 35 25 B-2 140° F. AC 370 B-2 28 days at 52 35 SAE-AMS-3281 140° F. Type 1 Class 70 days at 54 34 B-1/2 140° F. CS 3204 28 days at 41.1 pts 24.0 pts Class A-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F. CS 3204 28 days at 40.1 pts 23.3 pts Class B-2 140° F. SAE-AMS-S-8802 70 days at Type 2 140° F.

The data showed in Tables 5-9 demonstrate that the fuel of Example 1 has improved or comparable sealant compatibility compared with the commercially available fuel 100LL.

Further Sealant Testing

In this experiment, the Shore durometer was used for measuring the hardness of a range of polysulfide sealant materials after exposure to various fuel samples (according to ASTM D2240). The Shore Hardness Scale measures the hardness of polysulfides sealants that range from very soft, to medium, to hard. Higher numbers on the scale indicate greater resistance to indentation and thus harder materials. Lower numbers indicate softer materials.

Three different polysulfide sealants were tested in this experiment, namely AC350-B, PR1440-B and CS3204-B. Two different fuels were used in this experiment, namely Reference Fuel A and Example 1. The sealant was first applied to a metal coupon and allowed to cure. The coupon was then exposed to fuel at 135° F. The hardness of the sealant was then measured at various intervals (no fuel exposure, and after 96 hours, 192 hours, 288 hours and 408 hours of fuel exposure) using said durometer. The results are shown in Tables 10-12 below.

TABLE 10 (Hardness Measurements for AC350-B) 96 hrs 192 hrs 288 hrs 408 hrs No Fuel at at at at exposure 135° F. 135° F. 135° F. 135° F. Reference 18 14 10 10 10 Fuel A Example 1 18 15 14 14 14

TABLE 11 (Hardness Measurements for PR1440-B) 96 hrs 192 hrs 288 hrs 408 hrs No Fuel at at at at exposure 135° F. 135° F. 135° F. 135° F. Reference 18 14 10 10 10 Fuel A Example 1 18 15 14 14 14

TABLE 12 (Hardness Measurements for CS3204-B) 96 hrs 192 hrs 288 hrs 408 hrs No Fuel at at at at exposure 135° F. 135° F. 135° F. 135° F. Reference 14 11 7 8 8 Fuel A Example 1 14 13 11 11 11

FIG. 7 is a graphical representation of the data set out in Table 10 (where the sealant material is AC-350B)

FIG. 8 is a graphical representation of the data set out in Table 11 (where the sealant material is PR1440-B)

FIG. 9 is a graphical representation of the data set out in Table 12 (where the sealant material is CS3204-B)

As can be seen from Tables 10-12 and FIGS. 7-9 , the fuel of Example 1 provides significantly higher hardness measurements compared with Reference Fuel A. Maintaining a higher hardness means that the sealant is not being impacted in a negative way.

Comparative Examples 1-9

Further comparative examples (not according to the present invention) were prepared where the components were varied as provided below and their physical properties were measured and compared to the ASTM D910 specification for aviation fuels. For example, none of the Comparative Examples 1-3 and 6-9 contain any mesitylene which is a key component of the fuel compositions of the present invention. Further, Comparative Examples 4 and 5 contain significantly higher levels of mesitylene than required by the aviation gasoline fuels of the present invention. The difficulty in meeting many of the ASTM D-910 specifications is clear given the results below. As can been seen from the below examples, the variation in composition away from that of the present invention resulted in at least one of MON, T10, T90 or Freeze Point being outside of the ASTM D-910 specification.

Comparative Example 1

Light alkylate blend 66% v  Toluene 5% v Isopentane 4% v Isobutane 3% v Mesitylene 0% v Aniline 2% v t-butyl acetate 5% v p-xylene 15% v 

Property MON 99.20 RVP (kPa) 39.78 Freeze Point (deg C.) 0.0 Lead Content (g/gal) 0 T10 (deg C.) 84.3 T40 (deg C.) 100.6 T50 (deg C.) 103.1 T90 (deg C.) 126.2 FBP (deg C.) 152.5

Comparative Example 2

Light alkylate blend 66% v  Toluene 0% v Isopentane 4% v Isobutane 3% v Mesitylene 0% v Aniline 2% v t-butyl acetate 5% v p-xylene 20% v 

Property MON 99.10 RVP (kPa) 38.89 Freeze Point (deg C.) 0.0 Lead Content (g/ gal) 0.0 T10 (deg C.) 85.7 T40 (deg C.) 103.4 T50 (deg C.) 105.4 T90 (deg C.) 133.0 FBP (deg C.) 151.5

Comparative Example 3

Light alkylate 65% v  Toluene 0% v Isopentane 5% v Isobutane 3% v Mesitylene 0% v Aniline 2% v t-butyl acetate 5% v p-xylene 20% v 

Property MON 98.90 RVP (kPa) 40.4 Freeze Point (deg C.) 0.0 Lead Content (g/gal) 0.0 T10 (deg C.) 82.9 T40 (deg C.) 103.4 T50 (deg C.) 106.4 T90 (deg C.) 133.2 FBP (deg C.) 151.5

Comparative Example 4

Light alkylate 60% v  Toluene 5% v Isopentane 10% v  Isobutane 3% v Mesitylene 15% v  Aniline 2% v t-butyl acetate 5% v p-xylene 0% v

Property MON 98.50 RVP (kPa) 48.19 Freeze Point (deg C.) 0.0 Lead Content (g/gal) 0.0 T10 (deg C.) 70.0 T40 (deg C.) 100.3 T50 (deg C.) 102.4 T90 (deg C.) 156.7 FBP (deg C.) 160.5

Comparative Example 5

Light alkylate 61% v  Toluene 5% v Isopentane 8% v Isobutane 4% v Mesitylene 15% v  Aniline 2% v t-butyl acetate 5% v p-xylene 0% v

Property MON 99.20 RVP (kPa) 49.78 Freeze Point (deg C.) 0.0 Lead Content (g/gal) 0.0 T10 (deg C.) 71.0 T40 (deg C.) 101.5 T50 (deg C.) 104.5 T90 (deg C.) 155.0 FBP (deg C.) 172.5

Comparative Example 6

Light alkylate 62% v  Toluene 0% v Isopentane 8% v Isobutane 3% v Mesitylene 0% v Aniline 2% v t-butyl acetate 5% v p-xylene 20% v 

Property MON 98.9 RVP (kPa) 44.6 Freeze Point (deg C.) 0.0 Lead Content (g/gal) 0.0 T10 (deg C.) 74.5 T40 (deg C.) 103.0 T50 (deg C.) 105.5 T90 (deg C.) 134.0 FBP (deg C.) 152.0

Comparative Example 7

Light alkylate 62% v  Toluene 0% v Isopentane 9% v Isobutane 3% v Mesitylene 0% v Aniline 2% v t-butyl acetate 4% v p-xylene 20% v 

Property MON 100.00 RVP (kPa) 45.09 Freeze Point (deg C.) 0.5 Lead Content (g/ gal) 0.0 T10 (deg C.) 75.5 T40 (deg C.) 102.5 T50 (deg C.) 104.5 T90 (deg C.) 132.5 FBP (deg C.) 152.5

Comparative Example 8

Light alkylate 63% v  Toluene 0% v Isopentane 8% v Isobutane 3% v Mesitylene 0% v Aniline 2% v t-butyl acetate 4% v p-xylene 20% v 

Property ON 99.70 RVP (kPa) 42.68 Freeze Point (deg C.) 0.5 Lead Content (g/gal) 0.0 T10 (deg C.) 77.5 T40 (deg C.) 103.0 T50 (deg C.) 105.5 T90 (deg C.) 133.0 FBP (deg C.) 152.0

Comparative Example 9

Light alkylate 64% v  Toluene 0% v Isopentane 7% v Isobutane 3% v Mesitylene 0% v Aniline 2% v t-butyl acetate 4% v p-xylene 20% v 

Property MON 99.70 RVP (kPa) 41.09 Freeze Point (deg C.) 1.0 Lead Content (g/ gal) 0.0 T10 (deg C.) 80.2 T40 (deg C.) 103.9 T50 (deg C.) 105.9 T90 (deg C.) 131.5 FBP (deg C.) 154.0 

1. An unleaded aviation fuel composition having a MON of at least 99.6, sulfur content of less than 0.05 wt %, CHN content of at least 98 wt %, less than 2 wt % of oxygen content, an adjusted heat of combustion of at least 43.5 MJ/kg, a vapor pressure in the range of 38 to 49 kPa, comprising a blend comprising: from 5 vol. % to 25 vol. % of toluene having a MON of at least 107; from 0.5 vol. % to 4 vol. % of aniline; from 30 vol % to 70 vol % of at least one alkylate or alkyate blend having an initial boiling range of from 32° C. to 60° C. and a final boiling range of from 105° C. to 140° C., having T40 of less than 99° C., T50 of less than 100° C., T90 of less than 110° C., the alkylate or alkylate blend comprising isoparaffins from 4 to 9 carbon atoms, 3-20 vol % of C5 isoparaffins, 3-15 vol % of C7 isoparaffins, and 60-90 vol % of C8 isoparaffins, based on the alkylate or alkylate blend, and less than 1 vol % of C10+, based on the alkylate or alkylate blend; from 0.1 vol. % to 10 vol. % of branched alkyl acetate; at least 8 vol % of isopentane, isobutane, or mixture thereof in an amount sufficient to reach a vapor pressure in the range of 38 to 49 kPa; from 2 vol. % to 10 vol. % of mesitylene; wherein the fuel composition contains less than 1 vol % of C8 aromatics.
 2. An unleaded aviation fuel composition according to claim 1, wherein the total content of isopentane, isobutane or mixture thereof in the fuel composition is from 10 vol. % to 20 vol %.
 3. An unleaded aviation fuel composition according to claim 1 wherein the content of aniline is from 1 vol % to 3 vol %.
 4. An unleaded aviation fuel composition according to claim 1, wherein the volume ratio of branched alkyl acetate to aniline is at least 1.5:1.
 5. An unleaded aviation fuel composition according to claim 1 wherein the volume ratio of isopentane to isobutane is at least 2:1.
 6. An unleaded aviation fuel composition according to claim 1, further comprising an aviation fuel additive.
 7. An unleaded aviation fuel composition according to claim 1, having a freezing point of less than −58° C.
 8. An unleaded aviation fuel composition of claim 1, having a final boiling point of less than 190° C.
 9. An unleaded aviation fuel composition of claim 1, wherein the alkylate or alkylate blend have a C10+ content of less than 0.1 vol % based on the alkylate or alkylate blend.
 10. An unleaded aviation fuel composition of claim 1, wherein the branched alkyl acetate is t-butyl acetate.
 11. An unleaded aviation fuel composition of claim 1, having a final boiling point of at most 180° C.
 12. Use of an unleaded aviation fuel composition having a MON of at least 99.6, sulfur content of less than 0.05 wt %, CHN content of at least 98 wt %, less than 2 wt % of oxygen content, an adjusted heat of combustion of at least 43.5 MJ/kg, a vapor pressure in the range of 38 to 49 kPa, comprising a blend comprising: from 5 vol. % to 25 vol. % of toluene having a MON of at least 107; from 0.5 vol. % to 4 vol. % of aniline; from 30 vol % to 70 vol % of at least one alkylate or alkyate blend having an initial boiling range of from 32° C. to 60° C. and a final boiling range of from 105° C. to 140° C., having T40 of less than 99° C., T50 of less than 100° C., T90 of less than 110° C., the alkylate or alkylate blend comprising isoparaffins from 4 to 9 carbon atoms, 3-20 vol % of C5 isoparaffins, 3-15 vol % of C7 isoparaffins, and 60-90 vol % of C8 isoparaffins, based on the alkylate or alkylate blend, and less than 1 vol % of C10+, based on the alkylate or alkylate blend; from 0.1 vol. % to 10 vol. % of branched alkyl acetate; at least 8 vol % of isopentane, isobutane, or mixture thereof in an amount sufficient to reach a vapor pressure in the range of 38 to 49 kPa; from 2 vol. % to 10 vol. % of mesitylene; wherein the fuel composition contains less than 1 vol % of C8 aromatics; for the purpose of providing one or more of: (i) improved materials compatibility (ii) reduced elastomer swelling (iii) reduced paint staining (iv) improved engine endurance (v) reducing bladder delamination.
 13. An unleaded aviation fuel composition of claim 1, having a final boiling point of less than 180° C. 